In many industries it is necessary to deform and shape a thermoplastic projection of a workpiece as a part of a fastening or staking process. For example, in the automotive industry it is common for an emblem to be staked to the center of a steering wheel closeout. While earlier approaches to performing such staking activities involved the use of ultrasonics and hot air, ultrasonics typically produce part marking and hot air often results in damage due to over spray of the hot air.
As a result of the above limitations associated with ultrasonics and hot air, laser staking has evolved in many industries. In conventional laser staking approaches, a projection of a workpiece is deformed by applying a predetermined level of laser radiation and a predetermined weld force to the projection with a specialized dye. The predetermined weld force and the predetermined level of laser radiation cause the projection to melt and collapse into the shape of the dye. After a predetermined period of time, the laser radiation and weld force are discontinued, and the projection is allowed to solidify. After solidification, the staking process is complete and the workpiece is fixed to the adjacent part.
A particular area of potential improvement for the above laser staking process relates to what parameter is monitored to determine when to discontinue the laser radiation and weld force. Specifically, the above discussed weld time control strategies fail to take into account molding and environmental history variables for the parts being staked together. For example, various projections will exhibit varying amounts of collapse for a given weld force, laser radiation and staking time. The final assemblies would therefore have varying overall physical dimensions due to collapse inconsistencies. The present invention recognizes that the collapse distance of the projection is the parameter of most interest and in large part determines the strength and quality of the part connection. It is therefore highly desirable to provide a mechanism for controlling the laser staking process which takes into consideration the staking parameter of most interest, i.e., collapse distance. Such a mechanism would provide reduced rework costs and improved quality.
The difficulties relating to determining what parameter to monitor in order to determine when to discontinue the laser radiation and weld force are equally applicable in other areas of laser welding. For example, in through transmission infrared (TTIr) welding, a first part that is transparent to the laser radiation is welded to a second part that absorbs the radiation. The laser radiation raises the temperature of the absorbent material to a critical melting temperature and the pressure is applied to press the parts together. A weld or bond joins the parts as the melt cools. TTIr welding has widespread application due to its relatively rapid formation of the weld as well as the strength and uniformity of the joint. Thus, in TTIr welding the collapsed distance within the weld zone can be most representative of the strength and quality of the part connection. It is therefore also highly desirable to provide a mechanism for controlling TTIr welding which takes into consideration the welding parameter of most interest, i.e., the collapsed distance.